Lubricating compositions

ABSTRACT

A method of reducing low-speed pre-ignition (LSPI) in a direct-injected spark-ignited internal combustion engine comprising lubricating the crankcase of the engine with a composition comprising a combination of a molybdenum-containing additive and a boron-containing additive. Preferably, the composition comprises a calcium detergent providing a calcium content of at least  0.08  wt %, based on the weight of the lubricating oil composition.

FIELD OF THE INVENTION

The present invention concerns a method of reducing low-speedpre-ignition (LSPI) events in a direct-injection spark-ignitioncombustion engine comprising lubricating the crankcase of the enginewith a lubricating composition comprising a combination of amolybdenum-containing additive and a boron-containing additive.

BACKGROUND OF THE INVENTION

Market demand, as well as governmental legislation, has fed automotivemanufacturers to continuously improve fuel economy and reduce CO₂emissions across engine families, while simultaneously maintainingperformance (horsepower). Using smaller engines providing higher powerdensities, increasing boost pressure, by using turbochargers orsuperchargers to increase specific output and down-speeding the engineby using higher transmission gear ratios allowed by higher torquegeneration at lower engine speeds have allowed engine manufacturers toprovide excellent performance while reducing frictional and pumpinglosses. However, higher torque at lower engine speeds has been found tocause random pre-ignition in engines at low speeds, a phenomenon knownas Low Speed Pre-Ignition, or LSPI, resulting in extremely high cylinderpeak pressures, which can lead to catastrophic engine failure. Thepossibility of LSPI prevents engine manufacturers from fully optimizingengine torque at lower engine speed in such smaller, high-outputengines.

While not wishing to be bound by any specific theory, it is believedthat LSPI may be caused, at least in part, by auto-ignition of droplets,e.g. comprising engine oil, or a mixture of engine oil, fuel and/ordeposits, that enter the engine combustion chamber from the pistoncrevice (space between the piston ring pack and cylinder liner) underhigh pressure, during periods in which the engine is operating at lowspeeds, and compression stroke time is longest (e.g., an engine having a7.5 msec compression stroke at 4000 rpm may have a 24 msec compressionstroke when operating at 1250 rpm). Therefore, it would be advantageousto identify and provide lubricating oil compositions that are resistantto auto-ignition and therefore prevent or ameliorate the occurrence ofLSPI.

Some attempts have been made in the an to address this problem. Forexample, SAE 2013-01-2569 (“Investigation of Engine Oil Effect onAbnormal Combustion in Turbocharged Direct Injection-Spark IgnitionEngines (Part 2)”, Hirano et al.) concludes that increasing calciumconcentration leads to greater LSPI frequency. It is also concluded thatincreasing zinc dihydrocarbyl dithiophosphate (ZDDP) concentration canreduce LSPI frequency. SAE 2014-01-2785 (“Engine Oil Development forPreventing Pre-Ignition in Turbocharged Gasoline Engine”, Fujimoto etal) concludes that reducing the amount of calcium detergent in alubricating oil formulation is the most effective approach at reducingLSPI events. It is also concluded that increasing the amount of ZDDP canbe effective in reducing LSPI frequency, SAE 2015-01-2027 (“Engine OilFormulation Technology to Prevent Pre-Ignition in Turbocharged DirectInjection Spark Ignition Engines”, Onodera et al.) concludes that (a)reducing calcium, content together with increasing molybdenum content inengine oil formulations, and (b) substitution of calcium with magnesiumin detergents for engine oil formulations, were both effective inreducing the frequency of LSPI events. A method of reducing LSPIfrequency by using a lubricating oil having a reduced sodium content andcontaining certain molybdenum-containing compounds is disclosed inWO2017/011683. WO0015/171980 discloses a method of reducing LSPIfrequency by including in a lubricating oil formulation at least oneboron-containing compound, such as a borated dispersant or a mixture ofa boron-containing compound and a dispersant. However, according to theexamples disclosed in WO2015/171980, it was necessary to replace asubstantial amount, or even ail of, the calcium detergent with amagnesium detergent in order to obtain significant improvements in LSPIfrequency.

The prior art has further recognised that reducing the calcium content,and/or increasing the ZDDP content, of a lubricating oil formulation canlead to a reduction in LSPI events. However, detergents are oftenconsidered to be necessary additives for maintaining basic engine oilsperformance. Thus, recent efforts in providing lubricating oilformulations that reduce LSPI events have focused on replacing calciumdetergents with alternative detergents. However, alternative detergentscapable of providing appropriate detergent activity and adequate totalbase number (TBN) can be challenging to develop. Furthermore, increasedZDDP contents in lubricating oil formulations can lead to other, lessdesirable, effects. In particular, increasing ZDDP concentration oftenleads to an increase in ash formation and can lead to damage ofcatalysts in engine exhaust systems. EP 3 101 095 discloses alubricating oil composition for reducing LSPI frequency, the compositioncomprising a compound containing calcium and/or magnesium, a compoundcontaining molybdenum and/or phosphorus, and an ashless dispersioncontaining nitrogen, According to the disclosure of EP 3 101 095, LSPIevent frequency can be reduced by controlling the relative amounts ofcalcium, magnesium, molybdenum and phosphorus in the lubricating oilcomposition.

Thus, there remains a need for a lubricating oil composition suitablefor use in modern direct injection-spark ignition engines that reducesoccurrences of LSPI events.

SUMMARY OF THE INVENTION

The present inventors have surprisingly found that the use of bothmolybdenum-containing and boron-containing additives in a lubricatingoil composition significantly reduces in the frequency of LSPI events indirect injection-spark ignition internal combustion engines when thecrankcase of the engine is lubricated with said lubricating oilcomposition. More particularly, the present inventors have surprisinglyfound a synergistic improvement in LSPI reduction when using such alubricating composition as compared to using a lubricating oilcomposition comprising only molybdenum-containing additives and notboron-containing additives, and vice versa.

Thus, the present invention provides, according to a first aspect, amethod of reducing LSPI events in a direct-injection spark-ignitioninternal combustion engine comprising lubricating the crankcase of theengine with a lubricating oil composition, the composition comprising aboron-containing additive and a molybdenum-containing additive, having amolybdenum content of at least 150 ppm by weight, based on the weight ofthe lubricating oil composition, and having a boron content of at least150 ppm by weight, based on the weight of the lubricating oilcomposition.

According to a second aspect, the present invention provides the use ofa combination of the composition a boron-containing additive and amolybdenum-containing additive in a lubricating oil composition toreduce LSPI events, when the composition lubricates the crankcase of adirect injection-spark ignition internal combustion engine, wherein, themolybdenum-containing additive provides the lubricating oil compositionwith a molybdenum content of at least 150 ppm by weight, based on theweight of the lubricating oil composition, and the boron-containingadditive provides the lubricating oil composition with a boron contentof at least 150 ppm by weight, based on the weight of the lubricatingoil composition.

In this specification, the following words and expressions, if and whenused, have the meanings ascribed below:

“hydrocarbyl” means a chemical group of a compound that normallycontains only hydrogen and carbon atoms and that is bonded to theremainder of the compound directly via a carbon atom but that maycontain hetero atoms provided that they do not detract from theessentially hydrocarbyl nature of the group;

“oil-soluble” or “oil-dispersible”, or cognate terms, do not necessarilyindicate that the compounds or additives are soluble, dissolvable,miscible, or are capable of being suspended in the oil in allproportions. These do mean, however, that they are, for example, solubleor stably dispersible in oil to an extent sufficient to exert theirintended effect in the environment in which the oil in employed.Moreover, the additional incorporation of other additives may alsopermit incorporation of other additives may also permit incorporation ofhigher levels of a particular additive, if desired;

“major amount” mean in excess of 50 mass % of a composition;

“minor amount” means 50 mass % or less of a composition;

“antifoam” is a chemical additive that reduces and hinders the formationof foam in the lubricating oil composition, examples of commonly usedantifoams are polydimethylsiloxanes and other silicones, certainalcohols, stearates and glycols;

“TBN” means total base number as measured by ASTM D2896 in units of mgKOHg⁻¹;

“phosphorus content” is measured by ASTM D5185;

“molybdenum content” is measured by ASTM D5185;

“boron content” is measured by ASTM D5185;

“sulfur content” is measured by ASTM D2622; and,

“sulphated ash content” is measured by ASTM D874.

Also, it will be understood that various components used, essential aswell as optimal and customary, may react under conditions offormulation, storage or use and that the invention includes the use ofthe product obtainable or obtained as a result of any such reaction.Further, it is understood that any upper and lower quantity, range andratio limits set forth herein may be independently combined.Furthermore, the constituents of this invention may be isolated or bepresent within a mixture and remain within the scope of the invention.

It will of course be appreciated that features described in relation toone aspect of the present invention may be incorporated into otheraspects of the present invention. For example, the use of the inventionmay incorporate any of the features described with reference to themethod of the invention and vice versa.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the LSPI test results of Example 3 in matrix format.

DETAILED DESCRIPTION

Several terms exist for various forms of abnormal combustion in sparkignited internal combustion engines including knock, extreme knock(sometimes referred to as super-knock or mega-knock), surface ignition,and pre-ignition (ignition occurring prior to spark ignition). Extremeknock occurs in the same manner as traditional knock, but with increasedknock amplitude, and can be mitigated using traditional knock controlmethods. LSPI occurs at low speeds and high loads. In LSPI, initialcombustion is relatively slow and similar to normal combustion, followedby a sudden increase in combustion speed. LSPI is not a runawayphenomenon, unlike some other types of abnormal combustion. Occurrencesof LSPI are difficult to predict, but are often cyclical in nature.

LSPI is most likely to occur in direct-injected, boosted (turbochargedor supercharged), spark-ignited (gasoline) internal combustion enginesthat, in operation, generate a brake mean effective pressure level ofgreater than about 1,500 kPa (15 bar) (peak torque), such as at leastabout 1,800 kPa (18 bar), particularly at least about 2,000 kPa (20 bar)at engine speeds of from about 1000 to about 2500 rotations per minute(rpm), such as at engine speeds of from about 1000 to about 2000 rpm. Asused herein, brake mean effective pressure (BMEP) is the mean effectivepressure calculated from measured brake torque. The word “brake” denotesthe actual torque or power available at the engine flywheel, as measuredon a dynamometer. Thus, BMEP is a measure of the useful power output ofthe engine. BMEP is defined as the work accomplished during an enginecycle, divided by the engine swept volume; the engine torque normalizedby engine displacement and can be calculated using the followingformula:

BMEP=2πTn _(c) /V _(d)

where T is torque (Nm), n_(c) is the number of revolutions per cycle,V_(d) is displacement (m³). For a 4 stroke engine n_(c) is 2, for a 2stroke engine n_(c) is 1.

SAE 2014-01-2785 has concluded that LSPI event frequency is stronglyinfluenced by the calcium content of the lubricating oil composition,and that it is preferable to avoid lubricating composition calciumcontents of greater than 0.11 wt. %, based on the weight of thelubricating oil composition, in order to avoid excessive LSPI eventfrequency.

Surprisingly, the present inventors have found that the presence of acombination of molybdenum and boron in a lubricating oil formulation iseffective at reducing the occurrence of LSPI events. Unexpectedly, ithas been found that the combination of both molybdenum and boronprovides a synergistic improvement in LSPI event reduction, thefrequency reduction being greater than expected from analysing theperformance of lubricating oil compositions comprising only molybdenumand compositions comprising only boron. It has now been found that theoccurrence of LSPI in engines can be reduced by lubricating thecrankcase with lubricating oil compositions comprising at least 150 ppmby weight molybdenum and at least 150 ppm by weight boron, based on feeweight of the lubricating oil composition, compared to lubricating thecrankcase with lubricating oil compositions comprising less than 150 ppmby weight molybdenum and less than 150 ppm by weight boron.Surprisingly, the present inventors have found that the method and useof the first and second aspects of the invention is effective atreducing LSPI event frequency even when the lubricating oil compositioncomprises a significant amount of calcium, for example when thelubricating oil composition additionally comprises at least 0.08 wt %calcium, based on the weight of the lubricating oil composition.

Preferably, the engine of the method of the first aspect of theinvention, and/or the use of the second aspect of the invention, is anengine that generates a break mean effective pressure level of greaterthan 1,500 kPa, optionally greater than 2,000 kPa, at engine speeds offrom 1,000 to 2,500 rotations per minute (rpm), optionally from 1,000 to2,000 rpm.

Optionally, the lubricating oil composition of all aspects of theinvention comprises at least 175 ppm molybdenum, preferably at least 300ppm molybdenum, optionally at least 350 ppm molybdenum, such as at least500 ppm molybdenum, for example at least 700 ppm molybdenum, by weight,based on the weight of the lubricating oil composition. Optionally, thelubricating oil composition comprises no more than 1500 ppm molybdenum,preferably no more than 1400 ppm molybdenum, such as no more than 1200ppm molybdenum, for example no more than 1100 ppm molybdenum, optionallyno more than 1000 ppm molybdenum, by weight, based on the weight of thelubricating oil composition. Optionally, the lubricating oil compositioncomprises from ISO to 1500 ppm molybdenum, preferably from 175 to 1500ppm molybdenum, optionally from 300 to 1400 ppm molybdenum, such as from350 to 1200 ppm molybdenum, for example from 300 to 1100 ppm molybdenum,optionally from 700 to 1000 ppm molybdenum, by weight, based on theweight of the lubricating oil composition.

Optionally, the lubricating oil composition comprises at least 200 ppmboron, preferably at least 300 ppm boron, such as at least 400 ppmboron, by weight, based on the weight of the lubricating oilcomposition. Optionally, the lubricating oil composition comprises nomore than 1500 ppm boron, preferably no more than 1000 ppm boron, suchas no more than 800 ppm boron, by weight, based on the weight of thecomposition, Optionally, the lubricating oil composition comprises from150 to 1500 ppm boron, preferably from 200 to 1000 ppm boron, optionallyfrom 400 to 800 ppm boron, by weight, based on the weight of thelubricating oil composition.

It will be understood that the boron-containing additive may be anysuitable oil-soluble compound or oil-dispersible compound.Boron-containing additives may be prepared by reacting a boron compoundwith an oil-soluble or oil-dispersible additive or compound. Boroncompounds include boron oxide, boron oxide hydrate, boron trioxide,boron trifluoride, boron tribromide, boron trichloride, boron acid suchas boronic acid, boric acid, tetraboric acid and rnetaboric acid, boronhydrides, boron amides and various esters of boron acids, For example,the boron-containing additive may be one or more of a borateddispersant; a borated dispersant viscosity index improver; an alkalimetal or a mixed alkali metal or an alkaline earth metal borate; aborated overbased metal detergent; a borated epoxide; a borate ester; asulfurised borate ester; and a borate amide. Preferably, theboron-containing additive is one or more of a borated dispersant, aborate ester or a borated overbased metal detergent. Optionally, theborated overbased metal detergent, if present, is a borated overbasedmetal detergent having a TBN of at least 150, such as a boratedoverbased calcium detergent having a TBN of at least 150.

Borated dispersants may be prepared by boration of succinimide, succinicester, benzylamine and their derivatives, each of which has an alkyl oralkenyl group of molecular weight of 700 to 3000. Processes formanufacture of these additives are known to those skilled in the art. Apreferred amount of boron contained in these dispersants is 0.1 to 5mass % (especially 0.2 to 2 mass %). A particularly preferable borateddispersant is a succinimide derivative of boron, for example boratedpolyisobutenyl succinimide. An example of a borated dispersant is aborated polyisobutenyl succinimide wherein the average number molecularweight (M _(n)) of the polybutenyl backbone is in the range from 700 to1250. Additionally or alternatively, borated dispersants are made byborating the ashless dispersants described below, using known boratingmeans and techniques.

Ashless dispersants are non-metallic organic materials that formsubstantially no ash on combustion, in contrast to metal-containing, andhence ash-forming, materials. They comprise a long chain hydrocarbonwith a polar head, the polarity being derived from inclusion of, e.g. anO, P or N atom. The hydrocarbon is an oleophilic group that confersoil-solubility, having, for example 40 to 500 carbon atoms. Thus,ashless dispersants may comprise an oil-soluble polymeric hydrocarbonbackbone having functional groups that are capable of associating withparticles to be dispersed. Typically, dispersants comprise amine,alcohol, amide, or ester polar moieties attached to the polymer backboneoften via a bridging group. Ashless dispersants may be, for example,selected from oil-soluble salts, esters, ammo-esters, amides, imides,and oxazolines of long chain hydrocarbon-substituted mono- anddicarboxylic acids or their anhydrides; thiocarboxylate derivatives of along chain of hydrocarbons; long chain aliphatic hydrocarbons having apolyamine attached directly thereto, and Mannich condensation productsformed by condensing a long chain substituted phenol with formaldehydeand alkylene polyamine, such as described in U.S. Pat. No. 3,442,808.The oil-soluble polymeric hydrocarbon backbone is typically an olefinpolymer or polyene, especially a polymer comprising a major molar amount(i.e. greater than 50 mole %) of a C₂ to C₁₈ olefin (e.g. ethylene,propylene, butylenes, isobutylene, pentene, octane-1, styrene), andtypically a C₂ to C₅ olefin. The oil-soluble polymeric hydrocarbonbackbone may be homopolymeric (e.g. comprising a copolymer of ethyleneand an alpha-olefin such as propylene or butylenes, or a copolymer oftwo different alpha-olefins). A preferred class of olefin polymerscomprises polybutenes, specifically polyisobutenes (PIB) orpoly-n-butenes, such as may be prepared by polymerization of a C₄refinery stream. Other classes of olefin polymers include ethylenealpha-olefin (EAO) copolymers and alpha-olefin homo-and copolymers.

Ashless dispersants include, for example, derivatives of long chainhydrocarbon-substituted carboxylic acids, examples being derivatives ofhigh molecular weight hydrocarbyl-substituted succinic acid. Anoteworthy group of dispersants are hydrocarbon-substitutedsuccinimides, made, for example, by reacting the above acids (orderivatives) with a nitrogen-containing compound, advantageously apolyalkylene polyamine, such as polyethylene polyamine. Particularlypreferred are the reaction products of polyalkylene polyamines withalkenyl succinic anhydrides, such as described in U.S. Pat. No.3,202,678; 3,154,560; 3,172,892; 3,024,195, 3,024,237; 3,219,666; and3,216,936; and BE-A-66,875. Preferred dispersants arepolyalkene-substituted succinimides wherein the polyalkene group has anumber-average molecular weight in the range of 900 to 5,000. Thenumber-average molecular weight is measured by gel permeationchromatography (GPC). The polyalkene group may comprise a major molaramount (i.e. greater than 50 mole %) of a C₂ to C₁₈ alkene, e.g. ethene,propene, butene, iso butene, pentene, octane-1 and styrene. Preferably,the alkene is a C₂ to C₅ alkene; more preferably it is butene orisobutene, such as may be prepared by polymerisation of a C₄ refinerystream. Most preferably, the number average molecular weight of thepolyalkene group is in the range of 950 to 2,800.

The above ashless dispersants are post-treated with boron to form aborated dispersant in ways known in the art, such as described in U.S.Pat. Nos. 3,087,936, 3,254,025 and 5,430,105. Boration may for examplebe accomplished by treating an acyl nitrogen-containing dispersant witha boron compound selected from boron oxide, boron halides, boron acidsand esters of boron acids, in an amount sufficient to provide from about0.1 to about 20 atomic proportions of boron for each mole of ashlessdispersant.

Alkali metal and alkaline earth metal borates are generally hydratedparticulate metal borates, which are known in the art. Alkali metalborates include mixed alkali and alkaline earth metal borates. Thesemetal borates are available commercially. Representative patentsdescribing suitable alkali metal and alkaline earth metal borates andtheir methods of manufacture include U.S. Pat. No. 3,997,454; 3,819,521;3,853,772; 3,907,601; 3,997,454; and 4,089,790.

Borated amines may be prepared by reacting one or more of the aboveboron compounds with one or more of fatty amines, e.g., an amine havingfrom four to eighteen carbon atoms. They may be prepared by reacting theamine with the boron compound at a temperature in the range of from 50to 300° C., preferably from 100 to 250° C., and at a ratio from 3:1 to1:3 equivalents of amine to equivalents of boron compound.

Borated epoxides are generally the reaction product of one or more ofthe above boron compounds with at least one epoxide. The epoxide isgenerally an aliphatic epoxide having from 8 to 30, preferably from 10to 24, more preferably from 12 to 20, carbon atoms. Examples of usefulaliphatic epoxides include heptyl epoxide and octyl epoxide. Mixtures ofepoxides may also be used, for instance commercial mixtures of epoxideshaving from 14 to 16 carbon atoms and from 14 to 18 carbon atoms. Theborated fatty epoxides are generally known and are described in U.S.Pat. No. 4,584,115.

Borate esters may be prepared by reacting one or more of the above boroncompounds with one or more alcohols of suitable oleophilicity.Typically, the alcohols contain from 6 to 30, or from 8 to 24, carbonatoms. The methods of making such borate esters are known in the art.The borate esters cars be borated phospholipids. Such compounds, andprocesses for making such compounds, are described in EP-A-0 684 298.Examples of sulfurised borated esters are also known in the art: seeEP-A-0 285 455 and U.S. Pat. No. 6,028,210. Alternatively, it may bethat a borate ester is substantially absent in the lubricating oilcompositions of the method or use of the present invention.

Borated overbased metal detergents are known in the art where the boratesubstitutes the carbonate in the core either in part or in full. Borateddetergents may be prepared by any conventional method, for example, aborated detergent may be prepared by treating a metal detergent withboric acid. Suitable borated detergents and methods of preparing themare disclosed in U.S. Pat. No. 3,480,548, 3,679,584, 3,829,381,3,909,691 and 4, 965,004.

Preferably, at least a portion of the boron content of the lubricatingoil composition is provided by a boron-containing dispersant additive,such as a major portion. In an embodiment of the invention, 100 wt. % ofthe boron in the lubricating oil composition, based on the weight of theboron in the lubricating oil composition, is provided by one or moreboron-containing dispersant additives.

Alternatively or in addition, at least a portion of the boron content ofthe lubricating oil composition is provided by a borated detergent.

Additionally or alternatively, at least a portion of the boron contentof the lubricating oil composition is provided by a borate ester.

In an embodiment of the invention, at least a portion of the boroncontent of the lubricating oil composition is provided by aboron-containing compound that is not a dispersant, such as a majorportion.

Optionally, 100 wt % of the boron in the lubricating oil composition,based on the weight of the boron in the lubricating oil composition isprovided by one or more non-dispersant boron-containing compounds, suchas a borated detergent and/or a borate ester. Optionally, from 20 wt. %to 100 wt. %, preferably from 40 wt. % to 80 wt. %, such as from 50 wt.% to 70 wt. %, of the boron in the lubricating oil composition, based onthe weight of the boron in die lubricating oil composition, is providedby one or more borated detergent(s) and/or borate ester(s).

It will be understood that the molybdenum-containing additive may be anysuitable oil-soluble or oil-dispersible organo-molybdenum compound.Preferably, 100 wt. % of the molybdenum content of the lubricating oilcomposition is provided by an organo-molybdenum compound, based on theweight of the lubricating oil composition. Such molybdenum-containingadditives generally exhibit friction modifying properties when presentin a lubricating oil composition. Additionally or alternatively, suchmolybdenum-containing additives may also provide antioxidant andanti-wear credits to a lubricating oil composition.

To enable the molybdenum compound to be oil-soluble or oil-dispersible,one or more ligands are typically bonded to a molybdenum atom in thecompound. The bonding of the ligands includes bonding by electrostaticinteraction as in the case of a counter-ion and forms of bondingintermediate between covalent and electrostatic bonding. Ligands withinthe same compound may be differently bonded. For example, a ligand maybe covalently bonded and another ligand may be electrostatically bonded.Preferably, the or each ligand is monoanionic and examples of suchligands are dithiophosphates, dithiocarbamates, xanthates, carboxylates,thioxanthates, phosphates and hydrocarbyl, preferably alkyl, derivativesthereof.

The molybdenum-containing additive may be mono-, di-, tri- ortetra-nuclear. Di-nuclear and tri-nuclear molybdenum compounds arepreferred. In the event that the compound is polynuclear, the compoundcontains a molybdenum core consisting of non-metallic atoms, such assulfur, oxygen and selenium, preferably consisting essentially ofsulfur.

In a preferred embodiment, the molybdenum compound is amolybdenum-sulfur compound. Preferably, the ratio of the number ofmolybdenum atoms, for example, in the core in the event that themolybdenum-sulfur compound is a poly-nuclear compound, to the number ofmonoanionic ligands, which are capable of rendering the compoundoil-soluble or oil-dispersible, is greater than 1 to 1, such as at least3 to 2. The molybdenum-sulfur compound's oil-solubility oroil-dispersibility may be influenced by the total number of carbon atomspresent among all of the compound's ligands. The total number of carbonatoms present among all of the hydrocarbyl groups of the compound'sligands typically will be at least 21, e.g. 21 to 800, such as at least25, at least 30 or at least 35. For example, the number of carbon atomsin each alkyl group will generally range between 1 to 100, preferably 1to 40, and more preferably between 3 and 20.

Examples of suitable organo-molybdenum compounds include molybdenumdithiocarbamates, molybdenum dithiophosphates, molybdenumdithiophosphinates, molybdenum xanthates, molybdenum thioxanthates,molybdenum sulfides, and the like, and mixtures thereof. Particularlypreferred are molybdenum dithiocarbamates, molybdenumdialkyldithiophosphates, molybdenum alkyl xanthates and molybdenumalkylthioxanthates. An especially preferred organo-molybdenum compoundis a molybdenum dithiocarbamate. In an embodiment of the presentinvention the oil-soluble or oil-dispersible molybdenum compoundconsists of either a molybdenum dithiocarbamate or a molybdenumdithiophosphate or a mixture thereof, as the sole source of molybdenumatoms in the lubricating oil composition. In an alternative embodimentof the present invention the oil-soluble or oil-dispersible molybdenumcompound consists of a molybdenum dithiocarbamate, as the sole source ofmolybdenum atoms in the lubricating oil composition.

Suitable dinuclear or dimeric molybdenum dialkyldithiocarbamate arerepresented by the following formula:

R₁ through R₄ independently denote a straight chain, branched chain oraromatic hydrocarbyl group having 1 to 24 carbon atoms; and X₁ throughX₄independently denote an oxygen atom or a sulfur atom. The fourhydrocarbyl groups, R₁ through R₄, may be identical or different fromone another.

Other molybdenum-containing additives useful in the compositions of thisinvention are organo-molybdenum compounds of the formulae Mo(ROCS₂)₄ andMo(RSCS₂)₄, wherein R is an organo group selected from the groupconsisting of alkyl, aryl, aralkyl and alkoxyalkyl, generally of from 1to 30 carbon atoms, and preferably 2 to 12 carbon atoms and mostpreferably alkyl of 2 to 12 carbon atoms. Especially preferred are thedialkyldithiocarbamates of molybdenum.

In a preferred embodiment, the molybdenum-containing additive is anoil-soluble or oil-dispersible trinuclear molybdenum-sulfur compound,Examples of trinuclear molybdenum-sulfur compounds are disclosed inWO98/26030, WO99/31113, WO99/66013, EP-A-1 138 752, EP-A-1 138 686 andEuropean patent application no. 02078011, each of which are incorporatedinto the present description by reference, particularly with respect tothe characteristics of the molybdenum compound or additive disclosedtherein.

Suitable tri-nuclear organo-molybdenum compounds include those of theformula Mo₃S_(k)L_(n)Q_(z) and mixtures thereof wherein L areindependently selected ligands having organo groups with a sufficientnumber of carbon atoms to render the compound soluble or dispersible inthe oil n is from 1 to 4, k varies from 4 through 7, Q is selected fromthe group of neutral electron donating compounds such as water, amines,alcohols, phosphines, and ethers, and z ranges from 0 to 5 and includesnon-stoichiometric values. At least 21 total carbon atoms should bepresent among all the ligands' organo groups, such as at least 25, atleast 30, or at least 35 carbon atoms.

The ligands are independently selected from the group of:

and mixtures thereof, wherein X, X₁, X₂, and Y are independentlyselected from the group of oxygen and sulfur, and wherein R₁, R₂, and Rare independently selected from hydrogen and organo groups that may bethe same or different. Preferably, the organo groups are hydrocarbylgroups such as alkyl (e.g., in which the carbon atom attached to theremainder of the ligand is primary or secondary), aryl, substituted aryland ether groups. More preferably, each ligand has the same hydrocarbylgroup. Importantly, the organo groups of the ligands have a sufficientnumber of carbon atoms to render the compound soluble or dispersible inthe oil. For example, the number of carbon atoms in each group willgenerally range between about 1 to about 100, preferably from about 1 toabout 30, and more preferably between about 4 to about 20. Preferredligands include dialkyldithiophosphate, alkylxanthate, anddialkyldithiocarbamate, and of these dialkyldithiocarbamate is morepreferred. Organic ligands containing two or more of the abovefunctionalities are also capable of serving as ligands and binding toone or more of the cores. Those skilled in the art will realize thatformation of the compounds of the lubricating oil composition of thepresent invention requires selection of ligands having the appropriatecharge to balance the core's charge.

Particularly suitable molybdenum-containing additives include compoundshaving the formula Mo₃S_(k)L_(n)Q_(z), having cationic cores surroundedby anionic ligands and being represented by structures such as

and having net charges of +4. Consequently, in order to solubilize thesecores the total charge among ail the ligands must be −4. Fourmono-anionic ligands are preferred. Without wishing to be bound by anytheory, it is believed that two or more tri-nuclear cores may be boundor interconnected by means of one or more ligands and the ligands may bemultidentate. This includes the case of a multidentate ligand havingmultiple connections to a single core. It is believed that oxygen and/orselenium may be substituted for sulfur in the core(s).

Additionally or alternatively, particularly suitable trinuclearmolybdenum-containing additives may be represented by the formulaMo₃S_(k)E_(x)L_(n)A_(p)Q_(z), wherein:

k is an integer of at least 1;

E represents a non-metallic atom selected from oxygen and selenium;

x can be 0 or an integer, and preferably k+x is at least 4, morepreferably in the range of 4 to 10, such as 4 to 7, most preferably 4 or7;

L represents a ligand that confers oil-solubility or oil-dispersibilityon the molybdenum-sulfur compound, preferably L is a monoanionic ligand;

n is an integer in the range of 1 to 4;

A represents an anion other than L, if L is an anionic ligand;

p can be 0 or an integer;

Q represents a neutral electron-donating compound; and

z is in the range of 0 to 5 and includes non-stoichiometric values.

Those skilled in the art will realise that formation of the trinuclearmolybdenum-sulfur compound will require selection of appropriate ligands(L) and other anions (A), depending on, for example, fee number ofsulfur and E atoms present in the core, i.e. the total anionic chargecontributed by sulfur atom(s), E atom(s), if present, L and A, ifpresent, must be −12. Examples of Q include water, alcohol, amine, etherand phosphine. It is believed that the electron-donating compound, Q, ismerely present to fill any vacant coordination sites on the trinuclearmolybdenum-sulfur compound. Examples of A can be of any valence, forexample, monovalent and divalent and include disulfide, hydroxide,alkoxide, amide and, thiocyanate or derivative thereof; preferably Arepresents a disulfide ion. Preferably, L is monoanionic ligand, such asdithiophosphates, dithiocarbarnates, xanthates, carboxylases,thioxanthates, phosphates and hydrocarbyl, preferably alkyl, derivativesthereof. When n is 2 or more, the ligands can be the same or differentin an embodiment, independently of the other embodiments, k is 4 or 7, nis either 1 or 2, L is a monoanionic ligand, p is an integer to conferelectrical neutrality on the compound based on the anionic charge on Aand each of x and z is 0.

In a further embodiment, independently of the other embodiments, k is 4or 7, L is a monoanionic ligand, n is 4 and each of p, x and z is 0.

In another embodiment, the molybdenum-containing additive comprisestrinuclear molybdenum core and bonded thereto a ligand, preferably amono-aniomc ligand, such as a dithiocarbamate, capable of rendering thecore oil-soluble or oil-dispersible. For the avoidance of doubt, themolybdenum-containing additive may also comprise either negativelycharged molybdenum species or positively charged molybdenum species orboth negatively and positively charged molybdenum species.

The molybdenum-sulfur cores, for example, the structures depicted in (I)and (II) above, may be interconnected by means of one or more ligandsthat are multidentate, i.e. a ligand having more than one functionalgroup capable of binding to a molybdenum atom, to form oligomers.Molybdenum-sulfur additives comprising such oligomers are considered tofall within the scope of the fabricating oil compositions of thisinvention.

Oil-soluble or oil-dispersible tri-nuclear molybdenum-containingadditives can be prepared by reacting in the appropriateliquid(s)/solvent(s) a molybdenum source such as (NH₄)₂Mo₃Si₃.n(H₂O),where n varies between 0 and 2 and includes non-stoichiometric values,with a suitable ligand source such as a tetralkylthiuram disulfide.Other oil-soluble or dispersible tri-nuclear molybdenum-containingadditives can be formed during a reaction in the appropriate solvent(s)of a molybdenum source such as of (NH₄)₂Mo₃S₁₃.n (H₂O), a ligand sourcesuch as tetralkylthiuram disulfide, dialkyldithiocarbamate, ordialkyldithiophosphate, and a sulfur abstracting agent such as cyanideions, sulfite ions, or substituted phosphines. Alternatively, atri-nuclear molybdenum-sulfur halide salt such as [M′]₂[Mo₃S₇A₆], whereM′ is a counter ion, and A is a halogen such as Cl, Br, or I, may bereacted with a ligand source such as a dialkyldithiocarbamate ordialkyldithiophosphate in the appropriate liquid(s)/solvent(s) to forman oil-soluble or dispersible trinuclear molybdenum compound. Theappropriate liquid/solvent may be, for example, aqueous or organic,

A compound's oil solubility or dispersibility may be influenced by thenumber of carbon atoms in the ligand's organo groups. Preferably, atleast 21 total carbon atoms should be present among all the ligands'organo groups. Preferably, the ligand source chosen has a sufficientnumber of carbon atoms in its organo groups to render the compoundsoluble or dispersible in the lubricating composition.

Other examples of molybdenum compounds include molybdenum carboxylatesand molybdenum nitrogen complexes, both of which may be sulfurised.

Alternatively, the molybdenum-containing additive may be an acidicmolybdenum compound. These compounds will react with a basic nitrogencompound as measured by ASTM test D-664 or D-2896 titration procedureand are typically hexavalent. Included are molybdic acid, ammoniummolybdate, sodium molybdate, potassium molybdate, and other alkalinemetal molybdates and other molybdenum salts, e.g., hydrogen sodiummolybdate, MoOCl₄, MoO₂Br₂, Mo₂O₃Cl₆, molybdenum trioxide of similaracidic molybdenum compounds.

Alternatively, the lubricating oil compositions of the present inventioncan be provided with molybdenum by molybdenum/sulfur complexes of basicnitrogen compounds as described, for example, in U.S. Pat. Nos.4,263,152; 4,285,822; 4,283,295; 4,272,387; 4,265,773; 4,261,843;4,259,195 and 4,259,194; and WO 94/06897.

Optionally, the lubricating oil composition comprises one or moremolybdenum-containing compounds that is not a friction modifier additive(for example that is not used as a friction modifier additive).Optionally, at least a portion of the molybdenum content of thelubricating oil composition is provided by a molybdenum-containingcompound that is not a friction modifier, such as a major portion.

Optionally, the lubricating oil composition of all embodiments of thepresent invention has a calcium content of at least 0.08 wt %, based onthe weight of the lubricating oil composition. The lubricating oilcomposition of all aspects of the invention may have a calcium contentof at least 0.10 wt. %, preferably at least 0.15 wt. %, for example atleast 0.18 wt. %, based on the weight of the lubricating oilcomposition. Optionally, the lubricating oil composition of all aspectsof the invention has a calcium content of from 0.08 wt,% to 0.8 wt. %,preferably from 0.10 wt. % to 0,6 wt. %, for example from 0,15 wt. % to0,5 wt. %, such as from 0.18 wt. % to 0.3 wt. %, based on the weight ofthe lubricating oil composition. It will be appreciated that it isparticularly advantageous to utilise LSPI-reducing additives inlubricating oil compositions containing higher concentrations ofcalcium.

Optionally, the lubricating oil composition has a magnesium content ofno more than 0.12 wt. %, such as no more than 0.6 wt. %, for example nomore than 0.03 wt. %, based on the weight of the lubricating oilcomposition. Optionally, the lubricating oil composition issubstantially free from magnesium, for example having a magnesiumcontent of about 0.0 wt. %, based on the weight of the lubricating oilcomposition.

Lubricating oil compositions suitable for use as passenger ear motoroils conventionally comprise a major amount of oil of lubricatingviscosity and minor amounts of performance enhancing additives,including detergents. Metal-containing or ash-forming detergentsfunction as both detergents to reduce or remove deposits and as acidneutralizers or rust inhibitors, thereby reducing wear and corrosion andextending engine life. Detergents generally comprise a polar head with along hydrophobic tail. The polar head comprises a metal salt of anacidic organic compound. The salts may contain a substantiallystoichiometric amount of the metal in which case they are usuallydescribed as normal or neutral salts, and have a total base number orTBN (as can be measured by ASTM D2896) of from 0 to less than 150, suchas 0 to about 80 or 100. A large amount of a metal base may beincorporated by reacting excess metal compound (e.g., an oxide orhydroxide) with an acidic gas (e.g., carbon dioxide). The resultingoverbased detergent comprises neutralized detergent as the outer layerof a metal base (e.g. carbonate) micelle. Such overbased detergents havea TBN of 150 or greater, and typically will have a TBN of from 250 to450 or more.

Optionally, the lubricating oil composition comprises a detergent, forexample a calcium detergent. Optionally, the detergent is a boratedcalcium detergent. Examples of suitable borated calcium detergentsinclude, but are not limited to, one or more borated calcium sulfonatedetergent, one or more borated calcium salicylate detergent, or amixture thereof. Preferably, such borated calcium detergents areoverbased borated calcium detergents. Such borated calcium detergentsmay be prepared by any conventional method. For example, it may be thatthe borated calcium detergent is prepared by treating a calciumdetergent with boric acid. Suitable borated calcium detergents andmethods of preparing such borated calcium detergents are disclosed inU.S. Pat. No. 3,480,548, 3,679,584, 3,829,381, 3,909,691 and 4,965,004.Optionally, the detergent is an overbased calcium detergent, for examplehaving a Total Base Number (TBN) of at least 150, preferably at least200. Preferably, the overbased calcium detergent has a TBN of from 200to 450. It will be appreciated that the composition optionally includesone or more additional detergents, such as a detergent that is not anoverbased calcium detergent having a TBN of at least 150. For example,it may be that the composition comprises a detergent package comprisingthe overbased calcium detergent. The detergent is preferably used in anamount providing the lubricating oil composition with a TBN of fromabout 4 to about 10 mg KOH/g, preferably from about 5 to about 8 mgKOH/g. Preferably, overbased detergents based on metals other thancalcium are present in amounts contributing no greater than 80%, such asno greater than 50% or no greater than 40% of the TBN of the lubricatingoil composition contributed by overbased detergent. Preferably,lubricating oil compositions of the present invention containnon-calcium-based overbased ash-containing detergents in amountsproviding no greater than about 40% of the total TBN contributed to thelubricating oil composition by overbased detergent. Combinations ofoverbased calcium detergents may be used (e.g., comprising two or moreof an overbased calcium phenate, an overbased calcium salicylate and anoverbased calcium sulfonate; or comprising two or more calciumdetergents each having a different TBN of greater than 150). Preferably,the detergent will have, or have on average, a TBN of at least about200, such as front about 200 to about 500; preferably at least about250, such as from about 250 to about 500; more preferably at least about300, such as from about 300 to about 450.

Calcium detergents that may be used in all aspects of the presentinvention include, oil-soluble neutral and overbased sulfonates,phenates, sulfurized phenates, thiophosphonates, salicylates, andnaphthenates and other oil-soluble carboxylates of calcium. It will beappreciated that suitable calcium detergents may also comprise othermetals, particularly alkali or alkaline earth metals, e.g., barium,sodium, potassium, lithium, calcium, and/or magnesium. The most commonlyused additional metals are magnesium and sodium, either of which or bothmay be present in the calcium detergent and/or the borated calciumdetergent. The detergent may optionally comprise combinations ofdetergents, whether overbased or neutral or both.

Sulfonates may be prepared from sulfonic acids which are typicallyobtained by the sulfonation of alkyl substituted aromatic hydrocarbonssuch as those obtained from the fractionation of petroleum or by thealkylation of aromatic hydrocarbons. Examples include those obtained byalkylating benzene, toluene, xylene, naphthalene, diphenyl or theirhalogen derivatives such as chlorobenzene, chlorotoluene andchloronaphthalene. The alkylation may be carried out in the presence ofa catalyst with alkylating agents having from about 3 to more than 70carbon atoms. The alkaryl sulfonates usually contain from about 9 toabout 80 or more carbon atoms, preferably from about 16 to about 60carbon atoms per alkyl substituted aromatic moiety.

The oil soluble sulfonates or alkaryl sulfonic acids may be neutralisedwith oxides, hydroxides, alkoxides, carbonates, carboxylase, sulfides,hydrosulfides, nitrates, borates and ethers of the metal. The amount ofmetal compound is chosen having regard to the desired TBN of the finalproduct but typically ranges from about 100 to 220 mass % (preferably atleast 125 mass %) of that stoichiometrically required.

Metal salts of phenols and sulfurized phenols are prepared by reactionwith an appropriate metal compound such as an oxide or hydroxide andneutral or overbased products may be obtained by methods well known inthe art. Sulfurized phenols may be prepared by reacting a phenol withsulfur or a sulfur containing compound such as hydrogen sulfide, sulfurmonohalide or sulfur dihalide, to form products which are generallymixtures of compounds in which 2 or more phenols are bridged by sulfurcontaining bridges.

Carboxylate detergents, e.g., salicylates, can be prepared by reactingan aromatic carboxylic acid with an appropriate metal compound such asan oxide or hydroxide and neutral or overbased products may be obtainedby methods well known in the art. The aromatic moiety of the aromaticcarboxylic acid can contain hetero-atoms, such as nitrogen and oxygen.Preferably, the moiety contains only carbon atoms; more preferably themoiety contains six or more carbon atoms; for example benzene is apreferred moiety. The aromatic carboxylic acid may contain one or morearomatic moieties, such as one or more benzene rings, either fused orconnected via alkylene bridges. The carboxylic moiety may be attacheddirectly or indirectly to the aromatic moiety. Preferably the carboxylicacid group is attached directly to a carbon atom on the aromatic moiety,such as a carbon atom on the benzene ring. More preferably, the aromaticmoiety also contains a second functional group, such as a hydroxy groupor a sulfonate group, which can be attached directly or indirectly to acarbon atom on the aromatic moiety.

Preferred examples of aromatic carboxylic acids are salicylic acids andsulfurized derivatives thereof, such as hydrocarbyl substitutedsalicylic acid and derivatives thereof. Processes for sulfurizing, forexample a hydrocarbyl-substituted salicylic acid, are known to thoseskilled in the art. Salicylic acids are typically prepared bycarboxylation, for example, by the Kolbe-Schmitt process, of phenoxides,and in that case, will generally be obtained, normally in a diluent, inadmixture with uncarboxylated phenol.

Preferred substituents in oil-soluble salicylic acids are alkylsubstituents. In alkyl-substituted salicylic acids, the alkyl groupsadvantageously contain 5 to 100, preferably 9 to 30, especially 14 to20, carbon atoms. Where there is more than one alkyl group, the averagenumber of carbon atoms in all of the alkyl groups is preferably at least9 to ensure adequate oil solubility.

Detergents generally useful in the formulation of lubricating oilcompositions of the invention also include “hybrid” detergents formedwith mixed surfactant systems, e.g., phenate/salicylates,sulfonate/phenates, sulfonate/salicylates,sulfonates/phenates/salicylates, as described, for example, in U.S. Pat.Nos. 6,153,565; 6,281,179; 6,429,178; and 6,429,178.

Optionally, the detergent comprises a calcium phenate, a calciumsulfonate and/or a calcium salicylate. Optionally, the detergentcomprises a borated calcium phenate, a borated calcium sulfonate and/ora borated calcium salicylate, preferably a borated calcium salicylate.

Optionally, the detergent comprises a plurality of calcium detergents.Optionally, each calcium detergent is independently a calcium phenate, acalcium sulfonate or a calcium salicylate. Preferably, the detergent issubstantially free from any detergent that is not a calcium detergent.In other words, it may be that the detergent consists of one or morecalcium detergents. It will be appreciated that where a detergent issaid to be substantially free from anything other than a particular typeof detergent, or is said to consist of that particular type ofdetergent, the detergent may nevertheless comprise trace amounts ofanother material. For example, it may be that the detergent comprises atrace amount of another material left over from the preparation processused to make the detergent.

Optionally, at least 75 %, for example at least 90 %, such as at least95 %, of the calcium content of the lubricating oil composition isprovided by the detergent. It may be that when the calcium content ofthe lubricating composition is provided principally by the detergent,the detergent and LSPI characteristics of the composition can becontrolled particularly effectively.

Optionally, the composition additionally comprises a further detergent.Preferably, the further detergent is substantially free of calcium.Optionally, the farther detergent comprises one or more phenate,sulfonate and/or salicylate detergents, The further detergent may be anoverbased or neutral detergent. Optionally, the further detergentcomprises one or more neutral metal-containing detergents (having a TBNof less than 150). These neutral metal-based detergents may be magnesiumsalts or salts of other alkali or alkali earth metals, except calcium.Optionally, 100 % of the metal introduced into the lubricating oilcomposition by detergent is calcium. The further detergent may alsocontain ashless (metal-free) detergents such as oil-soluble hydrocarbylphenol aldehyde condensates described, for example, in US 2005/0277559A1.

Preferably, detergent in total is used In an amount providing thelubricating oil composition with from 0.2 to 2.0 mass %, such as from0.35 to 1.5 mass % or from 0.5 to 1.0 mass %, more preferably from about0.6 to about 0.8 mass % of sulfated ash (SASH).

Optionally, the composition comprises one or more additives from thelist consisting of: dispersants, corrosion inhibitors, antioxidants,pour point depressants, antifoaming agents, supplemental anti-wearagents, friction modifiers, and viscosity modifiers.

The oil of lubricating viscosity useful In the formulation oflubricating oil compositions suitable for use in the practice of theinvention may range in viscosity from light distillate mineral oils toheavy lubricating oils such as gasoline engine oils, mineral lubricatingoils and heavy duty diesel oils, Generally, the viscosity of the oilranges from about 2 mm²/sec (centistokes) to about 40 mm²/sec,especially from about 3 mm²/sec to about 20 mm²/sec, most preferablyfrom about 9 mm²/sec to about 17 mm²/sec, measured at 100° C.

Natural oils include animal oils and vegetable oils (e.g., castor oillard oil); liquid petroleum oils and hydrorefined, solvent-treated oracid-treated mineral oils of the paraffinic, naphthenic and mixedparaffinic-naphthenic types. Oils of lubricating viscosity derived fromcoal or shale also serve as useful base oils.

Synthetic lubricating oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as polymerized and interpolymerized olefins (e.g.,polybutylenes, polypropylenes, propylene-isobutylene copolymers,chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes),poly(1-decenes)); alkylbenzenes (e.g., dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes);polyphenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); andalkylated diphenyl ethers and alkylated diphenyl sulfides andderivatives, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof wherethe terminal hydroxyl groups have been modified by esterification,etherification, etc., constitute another class of known syntheticlubricating oils. These are exemplified by polyoxyalkylene polymersprepared by polymerization of ethylene oxide or propylene oxide, and thealky) and aryl ethers of polyoxyalkylene polymers (e.g.,methyl-polyiso-propylene glycol ether having a molecular weight of 1000or diphenyl ether of poly-ethylene glycol having a molecular weight of1000 to 1500); and mono- and polycarboxylic esters thereof, for example,the acetic acid esters, mixed C₃-C₈ fatty-acid esters and C₁₃ Oxo aciddiester of tetraethylene glycol.

Another suitable class of synthetic lubricating oils comprises theesters of dicarboxylic acids (e.g., phthalic acid, succinic acid, alkylsuccinic acids and alkenyl succinic acids, maleic acid, azelaic acid,suberic acid, sebasic acid, fumaric acid, adipic acid, linoleic aciddimer, malonic acid, alkylmalonic acids, alkenyl malonic acids) with avariety of alcohols (e.g., butyl alcohol, hexyl alcohol, dodecylalcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene glycolmonoether, propylene glycol). Specific examples of such esters includesdibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl fumarate, dioctylsebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate,didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyl diester oflinoleic acid dimer, and the complex ester formed by reacting one moleof sebacic acid with two moles of tetraethylene glycol and two moles of2-ethylhexanoic acid. Also useful are synthetic oils derived from a gasto liquid process from Fischer-Tropsch synthesized hydrocarbons, whichare commonly referred to as gas to liquid, or “GTL” base oils.

Esters useful as synthetic oils also include those made from C₅ to C₁₂monocarboxylic acids and polyols and polyol esters such as neopentylglycol, trimethylolpropaine, pentaerythritol, dipentaerythritol andtripentaerythritol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- orpolyaryloxysilicone oils and silicate oils comprise another useful classof synthetic lubricants; such oils include tetraethyl silicate,tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate,tetra-(4-methyl-2-ethylhexyl)silicate, tetra-(p-tert-butyl-phenyl)silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl)siloxanesand poly(methylphenyl)siloxanes. Other synthetic lubricating oilsinclude liquid esters of phosphorous-containing acids (e.g., tricresylphosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid)and polymeric tetrahydrofurans.

The oil of lubricating viscosity may comprise a Group I, Group II, GroupIII, Group IV or Group V base stocks or base oil blends of theaforementioned base stocks. Preferably, the oil of lubricating viscosityis a Group II, Group III, Group IV or Group V base stock, or a mixturethereof, or a mixture of a Group I base stock and one or more a GroupII, Group III, Group IV or Group V base stock. The base stock, or basestock blend preferably has a saturate content of at least 65%, morepreferably at least 75%, such as at least 85%. Preferably, the basestock or base stock blend is a Group III or higher base stock or mixturethereof, or a mixture of a Group II base stock and a Group III or higherbase stock or mixture thereof. Most preferably, the base stock, or basestock blend, has a saturate content of greater than 90 %. Preferably,the oil or oil blend will have a sulfur content of less than 1 mass %,preferably less than 0.6 mass %, most preferably less than 0.4 mass %,such as less than 0.3 mass %. In one preferred embodiment, at least 30mass %, preferably at least 50 mass more preferably at least 80 mass %of the oil of lubricating viscosity used in lubricating oil compositionsof the present invention is Group III base stock, a Group IV base stock,or a mixture of Group II and Group IV base stocks.

Preferably the volatility of the oil or oil blend, as measured by theNoack test (ASTM D5800), is less than or equal to 30 mass %, such asless than about 25 mass %, preferably less than or equal to 20 mass %,more preferably less than or equal to 15 mass %, most preferably lessthan or equal 13 mass %. Preferably, the viscosity index (VI) of the oilor oil blend is at least 85, preferably at least 100, most preferablyfrom about 105 to 140.

Definitions for the base stocks and base oils in the lubricating oilcompositions of this invention are the same as those found in theAmerican Petroleum Institute (API) publication “Engine Oil Licensing andCertification System”, Industry Services Department, Fourteenth Edition,December 1996, Addendum 1, December 1998. Said publication categorizesbase stocks as follows:

a) Group I base stocks contain less than 30 percent saturates and/orgreater than 0.03 percent sulfur and have a viscosity index greater thanor equal to 80 and less than 120 using the test methods specified inTable 1;

b) Group II base stocks contain greater than or equal to 90 percentsaturates and less than or equal to 0,03 percent sulfur and have aviscosity index greater than or equal to 80 and less than 120 using thetest methods specified in Table 1;

c) Group III base stocks contain greater than or equal to 90 percentsaturates and less than or equal to 0.03 percent sulfur and have aviscosity index greater than or equal to 120 using the test methodsspecified in Table 1;

d) Group IV base stocks are polyalphaoleflns (PAO); and,

e) Group V base stocks include all other base stocks not included inGroup I, III, III, or IV.

TABLE 1 Analytical Methods for Base Stock Property Test Method SaturatesASTM D 2007 Viscosity Index ASTM D 2270 Sulfur ASTM D 2622; ASTM D 4294;ASTM D 4927; ASTM D 3120

The lubricating oil compositions of all aspects of the present inventionmay further comprise a phosphorus-containing compound.

A suitable phosphorus-containing compound includes dihydrocarbyldithiophosphate metal salts, which are frequently used as anti-wear andantioxidant agents. The metal may be an alkali or alkaline earth metal,or aluminum, lead, tin, molybdenum, manganese, nickel or copper. Thezinc salts are most commonly used in lubricating oil in amounts of 0.1to 10, preferably 0.2 to 2 mass %, based upon the total weight of thelubricating oil composition. They may be prepared in accordance withknown techniques by first forming a dihydrocarbyl dithiophosphoric acid(DDPA), usually by reaction of one or more alcohol or a phenol with P₂S₅and then neutralizing the formed DDPA with a zinc compound. For example,a dithiophosphoric acid may be made by reacting mixtures of primary andsecondary alcohols. Alternatively, multiple dithiophosphoric acids canbe prepared where the hydrocarbyl groups on one are entirely secondaryin character and the hydrocarbyl groups on the others are entirelyprimary in character. To make the zinc salt, any basic or neutral zinccompound could be used but the oxides, hydroxides and carbonates aremost generally employed. Commercial additives frequently contain anexcess of zinc due to the use of an excess of the basic zinc compound inthe neutralization reaction.

The preferred zinc dihydrocarbyl dithiophosphates are oil soluble saltsof dihydrocarbyl dithiophosphoric acids and may be represented by thefollowing formula:

wherein R and R′ may be the same or different hydrocarbyl radicalscontaining from 1 to 18, preferably 2 to 12, carbon atoms and includingradicals such as alkyl, alkenyl, aryl, arylalkyl, alkaryl andcycloaliphatic radicals. Particularly preferred as R and R′ groups arealkyl groups of 2 to 8 carbon atoms. Thus, the radicals may, forexample, be ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl,amyl, n-hexyl, i-hexyl, n-octyl, decyl, dodecyl, octadecyl,2-ethylhexyl, phenyl, butylphenyl, cyclohexyl, methylcyclopentyl,propenyl, butenyl. In order to obtain oil solubility, the total numberof carbon atoms (i.e. R and R′) in the dithiophosphoric acid willgenerally be about 5 or greater, The zinc dihydrocarbyl dithiophosphate(ZDDP) preferably comprises zinc dialkyl dithiophosphates.

Lubricating oil compositions useful in the practice of the presentinvention will preferably contain a phosphorus-containing compound, inan amount introducing from 0.01 to 0.12 wt. % of phosphorus, such asfrom 0.04 to 0.10 wt. % of phosphorus, preferably, from 0.05 to 0.08 wt.% of phosphorus, based on the total mass of the lubricating oilcomposition into the lubricating oil composition. Optionally, thelubricating oil composition has a phosphorus content of no more than 0.1wt. % (1000 ppm), for example no more than 0.09 wt. % (900 ppm),preferably no more than 0.08 wt. % (800 ppm), based on the weight of thelubricating oil composition. In a preferred embodiment of the presentinvention, the lubricating oil composition has a phosphorous content ofno greater than 0.06 wt. % (600 ppm).

Oxidation inhibitors or antioxidants reduce the tendency of mineral oilsto deteriorate in service. Oxidative deterioration can be evidenced bysludge in the lubricant, varnish-like deposits on the metal surfaces,and by viscosity growth. Such oxidation inhibitors include hinderedphenols, alkaline earth metal salts of alkylphenolthioesters havingpreferably C₅ to C₁₂ alkyl side chains, calcium nonylphenol sulfide, oilsoluble phenates and sulfurized phenates, phosphosulfurized orsulfurized hydrocarbons or esters, phosphorous esters, metalthiocarbamates, oil soluble copper compounds as described in U.S. Pat.No. 4,867,890, and molybdenum-containing compounds.

Aromatic amines having at least two aromatic groups attached directly tothe nitrogen constitute another class of compounds that is frequentlyused for antioxidancy. Typical oil soluble aromatic amines having atleast two aromatic groups attached directly to one amine nitrogencontain from 6 to 16 carbon atoms. The amines may contain more than twoaromatic groups. Compounds having a total of at least three aromaticgroups in which two aromatic groups are linked by a covalent bond or byan atom or group (e.g., an oxygen or sulfur atom, or a —CO—, —SO₂— oralkylene group) and two are directly attached to one amine nitrogen arealso considered aromatic amines having at least two aromatic groupsattached directly to the nitrogen. The aromatic rings are typicallysubstituted by one or more substituents selected from alkyl, cycloalkyl,alkoxy, aryloxy, acyl, acylamino, hydroxy, and nitro groups. The amountof any such oil soluble aromatic amines having at least two aromaticgroups attached directly to one amine nitrogen should preferably notexceed 0.4 mass %.

Dispersants maintain in suspension materials resulting from oxidationduring use that are insoluble in oil, thus preventing sludgeflocculation and precipitation, or deposition on metal parts.Optionally, the lubricating oil compositions used according to thepresent invention comprise at least one dispersant, and may comprise aplurality of dispersants. The dispersant or dispersants are preferablynitrogen-containing dispersants and preferably contribute, in total,from 0.05 to 0.19 mass %, such as from 0.08 to 0.18 mass %, mostpreferably from 0.07 to 0.16 mass % of nitrogen to the lubricating oilcomposition.

Dispersants useful in the context of the present invention include therange of nitrogen-containing, ashless (metal-free) dispersants known tobe effective to reduce formation of deposits upon use in gasoline anddiesel engines, when added to lubricating oils and comprise an oilsoluble polymeric long chain backbone having functional groups capableof associating with particles to be dispersed. Typically, suchdispersants have amine, amine-alcohol or amide polar moieties attachedto the polymer backbone, often via a bridging group. The ashlessdispersant may be, for example, selected from oil soluble salts, esters,amino-esters, amides, imides and oxazolines of long chainhydrocarbon-substituted mono- and poly-carboxylic acids or anhydridesthereof; thiocarboxylate derivatives of long chain hydrocarbons; longchain aliphatic hydrocarbons having polyamine moieties attached directlythereto; and Mannich condensation products formed by condensing a longchain substituted phenol with formaldehyde and polyalkylene polyamine.

Generally, each mono- or dl-carboxylic acid-producing moiety will reactwith a nucleophilic group (amine or amide) and the number of functionalgroups in the polyalkenyl-substituted carboxylic acylating agent willdetermine the number of nucleophilic groups in the finished dispersant.

The polyalkenyl moiety of dispersants useful in the present inventionhas a number average molecular weight of from 700 to 3000, preferablybetween 950 and 3000, such as between 950 and 2800, more preferably fromabout 950 to 2500, and most preferably from 950 to 2400. In oneembodiment of the invention, the dispersant of the lubricating oilcomposition comprises a combination of a lower molecular weightdispersant (e.g., having a number average molecular weight of from 700to 1100) and a high molecular weight dispersant having a number averagemolecular weight of from at least 1500, preferably between 1800 and3000, such as between 2000 and 2800, more preferably from 2100 to 2500,and most preferably from 2150 to 2400. The molecular weight of adispersant is generally expressed in terms of the molecular weight ofthe polvalkenyl moiety as the precise molecular weight range of thedispersant depends on numerous parameters including the type of polymerused to derive the dispersant, the number of functional groups, and thetype of nucleophilic group employed.

The polyalkenyl moiety from which the high molecular weight dispersantsare derived preferably have a narrow molecular weight distribution(MWD), also referred to as polydispersity, as determined by the ratio ofweight average molecular weight (Mw) to number average molecular weight(Mn). Specifically, polymers from which dispersants useful in thepractice of the present invention are derived have a Mw/Mn of from 1.5to 2.0, preferably from 1.5 to 1.9, most preferably from 1.6 to 1.8.

Suitable hydrocarbons or polymers employed in the formation ofdispersants useful in the practice of the present invention includehomopolymers, interpolymers or lower molecular weight hydrocarbons. Onefamily of such polymers comprise polymers of ethylene and/or at leastone C₃ to C₂₈ alpha-olefin having the formula H₂C═CHR¹ wherein R¹ isstraight or branched chain alkyl radical comprising 1 to 26 carbon atomsand wherein the polymer contains carbon-to-carbon unsaturation,preferably a high degree of terminal ethenylidene unsaturation,Preferably, such polymers comprise interpolymers of ethylene and atleast one alpha-olefin of the above formula, wherein R¹ is alkyl of from1 to 18 carbon atoms, and more preferably is alkyl of from 1 to 8 carbonatoms, and more preferably still of from 1 to 2 carbon atoms. Therefore,useful alpha-olefin monomers and comonomers include, for example,propylene, butene-1, hexene-1, octene-1, 4-methylpentene-1, decene-1,dodecene-1, tridecene-1, tetradecene-1, pentadecene-1, hexadecene-1,heptadecene-1, octadecene-1, nonadecene-1, and mixtures thereof (e.g.,mixtures of propylene and butene-1, and the like). Exemplary of suchpolymers are propylene homopolymers, butene-1 homopolymers,ethylene-propylene copolymers, ethylene-butene-1 copolymers,propylene-butene copolymers and the like, wherein the polymer containsat least some terminal and/or internal unsaturation. Preferred polymersare unsaturated copolymers of ethylene and propylene and ethylene andbutene-1. The interpolymers may contain a minor amount, e.g. 0.5 to 5mole % of a C₄ to C₁₈ non-conjugated diolefin comonomer. However, it ispreferred that the polymers used in the practice of the presentinvention comprise only alpha-olefin homopolymers, interpolymers ofalpha-olefin comonomers and interpolymers of ethylene and alpha-olefincomonomers. The molar ethylene content of the polymers employed in thisinvention is preferably in the range of 0 to 80 and more preferably 0 to60 %. When propylene and/or butene-1 are employed as comonomer(s) withethylene, the ethylene content of such copolymer's is most preferablybetween 15 and 50 %, although higher or lower ethylene contents may bepresent.

These polymers may be prepared by polymerizing alpha-olefin monomer, ormixtures of alpha-olefin monomers, or mixtures comprising ethylene andat least one C₃ to C₂₈ alpha-olefin monomer, in the presence of acatalyst system comprising at least one metallocene (e.g., acyclopentadienyl-transition metal compound) and an alumoxane compound.Using this process, a polymer in which 95 % or more of the polymerchains possess terminal ethenylidene-type unsaturation can be provided.The percentage of polymer chains exhibiting terminal ethenylideneunsaturation may be determined by FTIR spectroscopic analysis,titration, or ¹³C NMR. Interpolymers of this latter type may becharacterized by the formula POLY-C(R¹)═CH₂ wherein R¹ is C₁ to C₂₆alkyl, preferably C₁ to C₁₈ alkyl, more preferably C₁ to C₈ alkyl andmost preferably C₁ to C₂ alkyl, (e.g., methyl or ethyl) and wherein POLYrepresents the polymer chain. The chain length of the R¹ alkyl groupwill vary depending on the comonomer(s) selected for use in thepolymerization. A minor amount of the polymer chains can containterminal ethenyl, i.e., vinyl, unsaturation, i.e., POLY-CH═CH₂, and aportion of the polymers can contain internal mono-unsaturation, e.g.POLY-CH═CH(R¹), wherein R¹ is as defined above. These terminallyunsaturated interpolymers may be prepared by known metallocene chemistryand may also be prepared as described in U.S. Pat. Nos. 5,498,809;5,663,130; 5,705,577; 5,814,715; 6,022,929 and 6,030,930.

Another useful class of polymers is polymers prepared by cationicpolymerization of isobutene, styrene, and the like. Common polymers fromthis class include polyisobutenes obtained by polymerisation of a C₄refinery stream having a butene content of 35 to 75 mass %, and anisobutene content of 30 to 60 mass %, in the presence of a Lewis acidcatalyst, stick as aluminum trichloride or boron trifluoride. Apreferred source of monomer for making poly-n-butenes is petroleumfeedstreams such as Raffinate II. These feedstocks are disclosed in theart such as in U.S. Pat. No. 4,952,739. Polyisobutylene is a mostpreferred backbone of the polymers useful in the practice of the presentinvention because it is readily available by cationic polymerizationfrom butene streams (e.g., using AlCl₃ or BF₃ catalysts). Suchpolyisobutylenes generally contain residual unsaturation in amounts ofabout one ethylenic double bond per polymer chain, positioned along thechain. A preferred embodiment utilizes polyisobutylene prepared from apure isobutylene stream or a Raffinate I stream to prepare reactiveisobutylene polymers with terminal vinylidene olefins. Preferably, thesepolymers, referred to as highly reactive polyisobutylene (HR-PIB), havea terminal vinylidene content of at least 65%, e.g., 70%, morepreferably at least 80%, most preferably, at least 85%. The preparationof such polymers is described, for example, in U.S. Pat. No. 4,152,499.HR-PIB is known and HR-PIB is commercially available under thetradenames Glissopal™ (from BASF).

Polyisobutylene polymers that may be employed are generally based on ahydrocarbon chain of from 700 to 3000. Methods for makingpolyisobutylene are known. Polyisobutylene can be functionalized byhalogenation (e.g. chlorination), the thermal “ene” reaction, or by freeradical grafting using a catalyst (e.g. peroxide), as described below.

The hydrocarbon or polymer backbone can be functionalized, e.g., withcarboxylic acid producing moieties (preferably acid or anhydridemoieties) selectively at sites of carbon-to-carbon unsaturation on thepolymer or hydrocarbon chains, or randomly along chains using any of thethree processes mentioned above or combinations thereof, in anysequence.

Processes for reacting polymeric hydrocarbons with unsaturatedcarboxylic acids, anhydrides or esters and the preparation ofderivatives from such compounds are disclosed in U.S. Pat. Nos,3,087,936; 3,172,892; 3,215,707; 3,231,587; 3,272,746; 3,275,554;3,381,022; 3,442,808; 3,565,804; 3,912,764; 4,110,349; 4,234,435;5,777,025; 5,891,953; as well as EP 0 382 450 B1; CA-1,335,895 andGB-A-1,440,219. The polymer or hydrocarbon may be functionalized, forexample, with carboxylic acid producing moieties (preferably acid oranhydride) by reacting the polymer or hydrocarbon under conditions thatresult in the addition of functional moieties or agents, i.e., acid,anhydride, ester moieties, etc., onto the polymer or hydrocarbon chainsprimarily at sites of carbon-to-carbon unsaturation (also referred to asethylenic or olefinic unsaturation) using the halogen assistedfunctionalization (e.g., chlorination) process or the thermal “ene”reaction.

Selective functionalization can be accomplished by halogenating, e.g.,chlorinating or brominating the unsaturated α-olefin polymer to about 1to 8 mass preferably 3 to 7 mass % chlorine, or bromine, based on theweight of polymer or hydrocarbon, by passing the chlorine or brominethrough the polymer at a temperature of 60 to 250° C., preferably 110 to160° C., e.g., 120 to 140° C., for about 0.5 to 10, preferably 1 to 7hours. The halogenated polymer or hydrocarbon (hereinafter backbone) isthen reacted with sufficient monounsaturated reactant capable of addingthe required number of functional moieties to the backbone, e.g.,monounsaturated carboxylic reactant, at 100 to 250° C., usually about180° C. to 235° C., for about 0.5 to 10, e.g., 3 to 8 hours, such thatthe product obtained will contain the desired number of moles of themonounsaturated carboxylic reactant per mole of the halogenatedbackbones. Alternatively, the backbone and the monounsaturatedcarboxylic reactant are mixed and heated while adding chlorine to thehot material.

While chlorination normally helps increase the reactivity of startingolefin polymers with monounsaturated functionalizing reactant, it is notnecessary with some of the polymers or hydrocarbons contemplated for usein the present invention, particularly those preferred polymers orhydrocarbons which possess a high terminal bond content and reactivity.Preferably, therefore, the backbone and the monounsaturatedfunctionality reactant, e.g., carboxylic reactant, are contacted atelevated temperature to cause an initial thermal “ene” reaction to takeplace. Ene reactions are known.

The hydrocarbon or polymer backbone can be functionalized by randomattachment of functional moieties along the polymer chains by a varietyof methods. For example, the polymer, in solution or in solid form, maybe grafted with the monounsaturated carboxylic reactant, as describedabove, in the presence of a free-radical initiator. When performed insolution, the grafting takes place at an elevated temperature in therange of about 100 to 260° C., preferably 120 to 240° C. Preferably,free-radical initiated grafting would be accomplished in a minerallubricating oil solution containing, e.g., 1 to 50 mass %, preferably 5to 30 mass % polymer based on the initial total oil solution.

The free-radical initiators that may be used are peroxides,hydroperoxides, and azo compounds, preferably those that have a boilingpoint greater than about 100° C. and decompose thermally within thegrafting temperature range to provide free-radicals. Representative ofthese free-radical initiators are azobutyronitrile,2,5-dimethylhex-3-ene-2, 5-bis-tertiary-butyl peroxide and dicumeneperoxide. The initiator, when used, typically is used in an amount ofbetween 0.005% and 1% by weight based on the weight of the reactionmixture solution. Typically, the aforesaid monounsaturated carboxylicreactant material and free-radical initiator are used in a weight ratiorange of from 1.0:1 to 30:1, preferably 3:1 to 6:1. The grafting ispreferably carried out in an inert atmosphere, such as under nitrogenblanketing. The resulting grafted polymer is characterized by havingcarboxylic acid (or ester or anhydride) moieties randomly attached alongthe polymer chains: it being understood, of course, that some of thepolymer chains remain un-grafted. The free radical grafting describedabove can be used for the other polymers and hydrocarbons useful in thepractice of the present invention.

The preferred monounsaturated reactants that are used to functionalizethe backbone comprise mono- and di-carboxylic acid material, i.e., acid,anhydride, or acid ester material, including (s) monounsaturated C₄ toC₁₀ dicarboxylic acid wherein (a) the carboxyl groups are vicinyl,(i.e., located on adjacent carbon atoms) and (b) at least one,preferably both, of said adjacent carbon atoms are part of said monounsaturation; (ii) derivatives of (i) such as anhydrides or C₁ to C₅alcohol derived mono- or diesters of (i); (iii) monounsaturated C₃ toC₁₀ monocarboxylic acid wherein the carbon-carbon double bond Isconjugated with the carboxy group, i.e., of the structure —C═C—CO—; and(iv) derivatives of (iii) such as C₁ to C₅ alcohol derived mono- ordiesters of (iii). Mixtures of monounsaturated carboxylic materials(i)-(iv) also may be used. Upon reaction with the backbone, themonounsaturation of the monounsaturated carboxylic reactant becomessaturated. Thus, for example, tnaleic anhydride becomesbackbone-substituted succinic anhydride, and acrylic acid becomesbackbone-substituted propionic acid. Exemplary of such monounsaturatedcarboxylic reactants are fumaric acid, itaconic acid, maleic acid,maleic anhydride, chloromaleic acid, chloromaleic anhydride, acrylicacid, methacrylic acid, crotonic acid, cinnamic acid, and lower alkyl(e.g., C₁ to C₄ alkyl) acid esters of the foregoing, e.g., methylmaleate, ethyl fumarate, and methyl fumarate.

To provide the required functionality, the monounsaturated carboxylicreactant, preferably maleic anhydride, typically will be used in anamount ranging from equimolar amount to about 100 mass % excess,preferably 5 to 50 mass % excess, based on the moles of polymer orhydrocarbon. Unreached excess monounsaturated carboxylic reactant can beremoved from the final dispersant product by, for example, stripping,usually under vacuum, if required.

The functionalized oil-soluble polymeric hydrocarbon backbone is thenderivatized with a nitrogen-containing nucleophilic reactant, such as anamine, aminoalcohol, amide, or mixture thereof, to form a correspondingderivative. Amine compounds are preferred. Useful amine compounds forderivatizing functionalized polymers comprise at least one amine and cancomprise one or more additional amine or other reactive or polar groups.These amines may be hydrocarbyl amines or may be predominantlyhydrocarbyl amines in which the hydrocarbyl group includes other groups,e.g., hydroxy groups, alkoxy groups, amide groups, nitrites, imidazolinegroups, and the like. Particularly useful amine compounds include mono-and polyamines, e.g., polyalkene and polyoxyalkylene polyamines of 2 to60, such as 2 to 40 (e.g., 3 to 20) total carbon atoms having 1 to 12,such as 3 to 12, preferably 3 to 9, most preferably form 6 to about 7nitrogen atoms per molecule. Mixtures of amine compounds mayadvantageously be used, such as those prepared by reaction of alkylenedihalide with ammonia. Preferred amines are aliphatic saturated amines,including, for example, 1,2-diammoethane; 1,3-diaminopropane;1,4-diaminobutane; 1,6-diaminohexane; polyethylene amines such asdiethylene triamine; methylene tetramine; tetraethylene pentamine; andpolypropyleneamines such as 1,2-propylene diamine; anddi-(1,2-propylene)triamine. Such polyamine mixtures, known as PAM, arecommercially available. Particularly preferred polyamine mixtures aremixtures derived by distilling the light ends from PAM products. Theresulting mixtures, known as “heavy” PAM, or HPAM, are also commerciallyavailable. The properties and attributes of both PAM and/or HPAM aredescribed, for example, in U.S. Pat. Nos. 4,938,881; 4,927,551;5,230,714; 5,241,003; 5,565,128; 5,756,431; 5,792,730; and 5,854,186.

Other useftil amine compounds include: alicyclic diamines such as1,4-di(aminomethyl) cyclohexane and heterocyclic nitrogen compounds suchas imidazolines. Another useful class of amines is the polyamido andrelated amido-amines as disclosed in U.S. Pat. Nos. 4,857,217:4,956,107;4,963,275; and 5,229,022. Also usable is tris(hydroxymethyl)aminomethane (TAM) as described in U.S. Pat. Nos. 4,102,798; 4,113,639;4,116,876; and UK Patent No. 989,409. Dendrimers, star-like amines, andcomb-structured amines may also be used. Similarly, one may usecondensed amines, as described in U.S. Pat. No, 5,053,152. Thefunctionalized polymer is reacted with the amine compound usingconventional techniques as described, for example, in U.S. Pat. Nos.4,234,435 and 5,229,022, as well as in EP-A-208,560.

A preferred dispersant composition is one comprising at least onepolyalkenyl succinimide, which is the reaction product of a polyalkenylsubstituted succinic anhydride (e.g., PIBSA) and a polyamine (PAM) thathas a coupling ratio of from 0.65 to 1.25, preferably from 0.8 to 1.1,most preferably from 0.9 to 1. In the context of this disclosure,“coupling ratio” may be defined as a ratio of the number of succinylgroups in the PIBSA to the number of primary amine groups in thepolyamine reactant.

Another class of high molecular weight ashless dispersants comprisesMannich base condensation products. Generally, these products areprepared by condensing about one mole of a long chain alkyl-substitutedmono- or polyhydroxy benzene with about 1 to 2.5 moles of carbonylcompound(s) (e.g., formaldehyde and paraformaldehyde) and about 0.5 to 2moles of polyalkylene polyamine, as disclosed, for example, in U.S. Pat.No. 3,442,808. Such Mannich base condensation products may include apolymer product of a metallocene catalyzed polymerization as asubstituent on the benzene group, or may be reacted with a compoundcontaining such a polymer substituted on a succinic anhydride in amanner similar to that described in U.S. Pat. No. 3,442,808. Examples offunctionalized and/or derivatized olefin polymers synthesized usingmetallocene catalyst systems are described in the publicationsidentified supra.

The dispersant(s) are preferably non-polymeric (e.g., are mono- orbis-succinimides). The dispersants), particularly the lower molecularweight dispersants, may optionally be borated. Such dispersants can beborated by conventional means, as generally taught in U.S. Pat. Nos.3,087,936, 3,254,025 and 5,430,105. Boration of the dispersant isreadily accomplished by treating an acyl nitrogen-containing dispersantwith a boron compound such as boron oxide, boron halide, boron acids,and esters of boron acids, in an amount sufficient to provide from 0.1to 20 atomic proportions of boron for each mole of acylated nitrogencomposition.

Dispersants derived from highly reactive polyisobutylene have been foundto provide lubricating oil compositions with a wear credit relative to acorresponding dispersant derived from conventional polyisobutylene. Thiswear credit is of particular importance in lubricants containing reducedlevels of ash-containing anti-wear agents, such as ZDDP. Thus, in onepreferred embodiment, at least one dispersant used in the lubricatingoil compositions of the present invention is derived from highlyreactive polyisobutylene.

Additional additives may be incorporated into the lubricating oilcomposition to enable particular performance requirements to be met.Examples of additives which may be included in the lubricating oilcompositions of the present invention are metal rust inhibitors,viscosity index improvers, corrosion inhibitors, oxidation inhibitors,friction modifiers, antifoaming agents, anti-wear agents and pour pointdepressants. Some are discussed in further detail below.

Friction modifiers and fuel economy agents that are compatible with theother ingredients of the final oil may also be included. Examples ofsuch materials include glyceryl monoesters of higher fatty acids, forexample, glyceryl mono-oleate; esters of long chain polycarboxylic acidswith diols, for example, the butane diol ester of a dimerizedunsaturated fatty acid; oxazoline compounds; and alkoxylatedalkyl-substituted mono-amines, diamines and alkyl ether amines, forexample, ethoxylated tallow amine and ethoxylated tallow ether amine.

The viscosity index of the base stock is increased, or improved, byincorporating therein certain polymeric materials that function asviscosity modifiers (VM) or viscosity index improvers (VII). Generally,polymeric materials useful as viscosity modifiers are those havingnumber average molecular weights (Mn) of from about 5,000 to about250,000, preferably from about 15,000 to about 200,000, more preferablyfrom about 20,000 to about 150,000. These viscosity modifiers can begrafted with grafting materials such as, for example, maleic anhydride,and the grafted material can be reacted with, for example, amines,amides, nitrogen-containing heterocyclic compounds or alcohol, to formmultifunctional viscosity modifiers (dispersant-viscosity modifiers).Polymer molecular weight, specifically Mn, can be determined by variousknown techniques. One convenient method is gel permeation chromatography(GPC), which additionally provides molecular weight distributioninformation (see W. W. Yau, J. J. Kirkland and D. D. Bly, “Modern SizeExclusion Liquid Chromatography”, John Wiley and Sons, New York, 1979).Another useful method for determining molecular weight, particularly forlower molecular weight polymers, is vapor pressure osmometry (see, e.g.,ASTM D3592).

One class of diblock copolymers useful as viscosity modifiers has beenfound to provide a wear credit relative to, for example, olefincopolymer viscosity modifiers. This wear credit is of particularimportance in lubricants containing reduced levels of ash-containinganti-wear agents, such as ZDDP. Thus, in one preferred embodiment, atleast one viscosity modifier used in the lubricating oil compositions ofthe present invention is a linear diblock copolymer comprising one blockderived primarily, preferably predominantly, from vinyl aromatichydrocarbon monomer, and one block derived primarily, preferablypredominantly, from diene monomer. Useful vinyl aromatic hydrocarbonmonomers include those containing from 8 to about 16 carbon atoms suchas aryl-substituted styrenes, alkoxy-substituted styrenes, vinylnaphthalene, alkyl-substituted vinyl naphthalenes and the like. Dienes,or diolefins, contain two double bonds, commonly located in conjugationin a 1,3 relationship. Olefins containing more than two double bonds,sometimes referred to as polyenes, are also considered within thedefinition of “diene” as used herein. Useful dienes include thosecontaining from 4 to about 12 carbon atoms, preferably from 8 to about16 carbon atoms, such as 1,3-butadiene, isoprene, piperylene,methylpentadiene, phenylbutadiene, 3,4-dimethyl-1,3-hexadiene,4,5-diethyl-1,3-octadiene, with 1,3-butadiene and isoprene beingpreferred.

As used herein in connection with polymer block composition,“predominantly” means that the specified monomer or monomer type that isthe principle component in that polymer block is present in an amount ofat least 85 % by weight of the block.

Polymers prepared with diolefins will contain ethylenic unsaturation,and such polymers are preferably hydrogenated. When the polymer ishydrogenated, the hydrogenation may be accomplished using any of thetechniques known in the prior art. For example, the hydrogenation may beaccomplished such that both ethylenic and aromatic unsaturation isconverted (saturated) using methods such as those taught, for example,in U.S. Pat. Nos. 3,113,986 and 3,700,633 or the hydrogenation may beaccomplished selectively such that a significant portion of theethylenic unsaturation is converted while little or no aromaticunsaturation is converted as taught, for example, in U.S. Pat. Nos.3,634,595; 3,670,054; 3,700,633 and U.S. Re 27,145. Any of these methodscan also be used to hydrogenate polymers containing only ethylenicunsaturation and which are free of aromatic unsaturation.

The block copolymers may include mixtures of linear diblock polymers asdisclosed above, having different molecular weights and/or differentvinyl aromatic contents as well as mixtures of linear block copolymershaving different molecular weights and/or different vinyl aromaticcontents. The use of two or more different polymers may be preferred toa single polymer depending on the rheological properties the product isintended to impart when used to produce formulated engine oil. Examplesof commercially available styrene/hydrogenated isoprene linear diblockcopolymers include Infineum SV140™, Infineum SV150™ and Infineum SV160™,available from Infineum USA L.P. and Infineum UK Ltd.; Lubrizol® 7318,available from The Lubrizol Corporation; and Septon 1001™ and Septon1020™, available from Septon Company of America (Kuraray Group).Suitable styrene/1,3-butadiene hydrogenated block copolymers are soldunder due tradename Glissoviscal™ by BASF.

Pour point depressants (PPD), otherwise known as lube oil flow improvers(LOFls) lower the temperature. Compared to VM, LOFIs generally have alower number average molecular weight. Like VM, LOFIs can be graftedwith grafting materials such as, for example, maleic anhydride, and thegrafted material can be reacted with, for example, amines, amides,nitrogen-containing heterocyclic compounds or alcohol, to formmultifunctional additives.

In the lubricating oil compositions of the present invention it may benecessary to include an additive which maintains the stability of theviscosity of the blend. Thus, although polar group-containing additivesachieve a suitably low viscosity in the pre-blending stage it has beenobserved that some compositions increase in viscosity when stored forprolonged periods. Additives which are effective in controlling thisviscosity increase include the long chain hydrocarbons functionalized byreaction with mono- or dicarboxylic acids or anhydrides which are usedin the preparation of the ashless dispersants as hereinbefore disclosed,In another preferred embodiment, the lubricating oil compositions of thepresent invention contain an effective amount of a long chainhydrocarbons functionalized by reaction with mono- or dicarboxylic acidsor anhydrides.

When lubricating compositions contain one or more of the above-mentionedadditives, each additive is typically blended into the base oil in anamount that enables the additive to provide its desired function.Representative effective amounts of such additives, when used incrankcase lubricants, are listed below. All the values listed (with theexception of detergent values) are stated as mass percent activeingredient (A.I). As used herein, A.I. refers to additive material thatis not diluent or solvent.

MASS % MASS % ADDITIVE (Broad) (Preferred) Dispersant 0.1-20   1-8 MetalDetergents 0.1-15  0.2-9  Corrosion Inhibitor 0-5   0-1.5 MetalDihydrocarbyl Dithiophosphate 0.1-6  0.1-4  Antioxidant 0-5 0.01-2.5Pour Point Depressant 0.01-5   0.01-1.5 Antifoaming Agent 0-5 0.001-0.15Supplemental Anti-wear Agents  0-1.0   0-0.5 Friction Modifier 0-5  0-1.5 Viscosity Modifier 0.01-10  0.25-3  Base stock Balance Balance

It may be desirable, although not essential to prepare one or moreadditive concentrates comprising additives (concentrates sometimes beingreferred to as additive packages) whereby several additives can be addedsimultaneously to the oil to form the lubricating oil composition.

The final composition may employ from 5 to 25 mass %, preferably 5 to 22mass %, typically 10 to 20 mass % of the concentrate, the remainderbeing oil of lubricating viscosity.

Preferably, the Noack volatility of the folly formulated lubricating oilcomposition (oil of lubricating viscosity plus all additives) will be nogreater than 20 mass %, such as no greater than 15 mass %, preferably nogreater than 13 mass %.

Lubricating oil compositions useful in the practice of the presentinvention may have an overall sulfated ash content of from 0.3 to 1,2mass %, such as from 0.4 to 1.1 mass preferably from 0.5 to 1.0 mass %.

This invention will be further understood by reference to the followingexamples, wherein all parts are parts by mass, unless otherwise notedand which include preferred embodiments of the invention.

DESCRIPTION OF THE EXAMPLES

Whilst the present invention has been described and illustrated withreference to particular embodiments, it will be appreciated by those ofordinary skill in the art that the invention lends itself to manydifferent variations not specifically illustrated herein. By way ofexample only, certain possible variations will now be described.

The amounts of additives provided are additive amounts including diluentoil, amounts unless otherwise indicated.

Example 1

Two SAE 0W-20 grade lubricating oil compositions representing typicalEuropean mid-SAPS passenger car motor oils were prepared. Theformulation of these compositions is shown in Table 2 below.

TABLE 2 Constituent Type Oil 1 Oil 2 Borated Dispersant ¹ 0.0057 0.0195(B, mass %) Mg Salicylate Detergent ² 0.02 0.02 (Mg, mass %) CaSalicylate Detergent ³ 0.15 0.15 (Ca, mass %) Molybdenum Compound ⁴ 00.0198 (Mo, mass %) Additive Package ⁵ 8.053 8.053 (mass %) SN150Diluent (mass %) 1.82 1.9 Pour Point Depressant⁶ 0.3 0.3 (mass %)Viscosity 9.5 9.5 Modifier⁷(mass %) Base Stock⁸(mass %) 77.5 76 SASH,mass % 0.73 0.75 P %, mass % 0.085 0.085 S %, mass % 0.2 0.2 ¹ Theborated dispersant was a borated polyisobutenyl succinimide dispersantavailable from Infineum UK Limited. ² The magnesium detergent was amagnesium salicylate detergent having a total base number of 342available from Infineum UK Limited. ³ The calcium detergent was the samefor each oil and comprised a mixture of a calcium salicylate detergenthaving a total base number of 225 available from Infineum UK Limited anda calcium salicylate detergent having a total base number of 64available from Infineum UK Limited. ⁴ The molybdenum dithiocarbamate isa trimeric molybdenum dithiocarbamate available from Infineum UKLimited. ⁵ The additive package was the same for each oil and includednon-borated dispersant, zinc dialkyldithiophosphate, aminic antioxidantand silicon antifoam. ⁶The pour point depressant was Infineum V385available from Infineum UK Ltd. ⁷The viscosity modifier was InfineumSV603 available from Infineum UK Ltd. ⁸The base stock comprised APIGroup III base oil.

Oil 1, being a comparative example, includes a typical dose of a borateddispersant, the oil composition having a boron content of 57 ppm, and nomolybdenum-containing additive. Oil 2, being an example of theinvention, includes a higher dose of a borated dispersant, the oilcomposition having a boron content of 195 ppm, and a molybdenumcontaining compound providing the oil composition with 198 ppm ofmolybdenum.

The oils were tested for LSPI event occurrence according to the GM LSP1test for approvals against Dexos™ specifications, the results beingpresented in Table 3. The test limit for the Dexos test for five runs is0 0 0 2 2, meaning that a composition achieving zero LSPI events in runs1, 2 and 3 and two or fewer LSPI events in runs 4 and 5, passes thetest, whereas a composition with more than zero LSPI events in runs 1, 2and/or 3 and/or more than two LSPI events in runs 4 and 5 fails thetest.

TABLE 3 LSPI Events Per Run Run Oil 1 Oil 2 1 1 0 2 1 0 3 3 0 4 3 0 5 41

Across all five runs with each composition, Oil 2 showed a lower LSPIevent frequency, passing the Dexos™ test, whereas Oil 1 failed theDexos™ test. These results indicate that a combined increase in bothboron and molybdenum contents provides a reduction in LSPI eventfrequency.

Example 2

Two further SAE 0W-20 grade lubricating oil compositions representingtypical European mid-SAPS passenger car motor oils with a phosphorouscontent of 0.09 mass % were prepared. The formulation of thesecompositions is shown in Table 4 below.

TABLE 4 Constituent Type Amount Oil 3 Oil 4 Borated Dispersant⁹ B, mass% 0.0037 0.0198 Ca Salicylate Detergent ¹⁰ Ca, mass % 0.18 0.18Molybdenum compound ¹¹ Mo, mass % 0.0027 0.0330 Additive package ¹² mass% 8.254 8.254 APP150DIL Diluent mass % 2.485 2.485 Pour PointDepressant¹³ mass % 0.300 0.300 Viscosity Modifier¹⁴ mass % 9.000 9.000Base Stock¹⁵ mass % 77.376 75.586 ⁹The borated dispersant was a boratedpolyisobutenyl succinimide dispersant available from Infineum UKLimited. ¹⁰ The calcium detergent comprised a calcium salicylatedetergent having a total base number of 225 available from Infineum UKLimited. ¹¹ The molybdenum dithiocarbamate is a trimeric molybdernumdithiocarbamate available from Infineum UK Limited. ¹² The additivepackage was the same for each oil and included non-borated dispersant,zinc dialkyldithiophosphate, aminic antioxidant, hindered phenolantioxidant, ashless friction modifier and silicon antifoam. ¹³The pourpoint depressant was Infineum V385 available from Infineum UK Ltd. ¹⁴Theviscosity modifier was Infineum SV603 available from Infineum UK Ltd.¹⁵The base stock comprised GTL base oil.

It can be seen from Table 4 that Oil 3 has a lower boron content and alower molybdenum content than Oil 4 composition.

The compositions were tested for LSPI event occurrence according to theASTM (Ford) LSPI test for applications claiming Gf-6/API SP, the resultsbeing presented in Table 6.

TABLE 5 LSPI Events Per Run Run Oil 3 Oil 4 1 7 4 2 17 2 3 12 4 4 10 4

Across all four runs with each composition, Oil 4 showed a significantlylower LSPI event frequency than Oil 3, indicating that an increase inboth boron and molybdenum content provides a reduction in LSPI eventfrequency.

Example 3

Five 5W-30 grade lubricating oil representing typical European mid-SAPSpassenger car motor oils were prepared. The formulation of thesecompositions is shown in Table 6 below.

TABLE 6 Constituent Type Amount Oil 5 Oil 6 Oil 7 Oil 8 Oil 9 Borated B,mass % 0.000 0.000 0.040 0.040 0.020 Dispersant¹⁶ Non-Borated mass %2.75 2.75 1.30 1.30 2.00 Dispersant¹⁷ Ca Sulfonate Ca, 0.151 0.151 0.1510.151 0.151 Detergent¹⁸ mass % MgSulfonate Mg, 0.030 0.030 0.030 0.0300.030 Detergent¹⁹ mass % Molybdenum Mo, 0.000 0.070 0.000 0.070 0.035Compound²⁰ mass % Additive mass % 3.103 3.103 3.103 3.103 3.103Package²¹ Group II mass % 1.00 1.00 1.00 1.00 1.00 Diluent Pour Pointmass % 0.30 0.30 0.30 0.30 0.30 Depressant²² Viscosity mass % 8.20 8.208.20 8.20 8.20 Modifier²³ Base Stock²⁴ mass % balance balance balancebalance balance SASH mass % 0.72 0.72 0.75 0.75 0.73 P % mass % 0.060.06 0.06 0.06 0.06 S % mass % 0.1 0.3 0.1 0.3 0.2 ¹⁶The borateddispersant was a borated polyisobutenyl succinimide dispersant availablefrom Infineum UK Limited. ¹⁷The non-borated dispersant was apolyisobutylene succinimide dispersant available from Infineum UKLimited. The amount of non-borated dispersant varies in order to balancethe varied amount of borated dispersant used to vary the amount of boronpresent in the oils. ¹⁸The calcium detergent comprised a calciumsulfonate detergent having a total base number of 300 available fromInfineum UK Limited. ¹⁹The magnesium detergent is a magnesium sulfonatedetergent having a total base number of 400 available from Infineum UKLimited. ²⁰The molybdenum dithiocarbamate is a trimeric molybdenumdithiocarbamate available from Infineum UK Limited. ²¹The additivepackage was the same for each oil and included zincdialkyldithiophosphate, aminic antioxidant, hindered phenol antioxidant,ashless friction modifier, diluent oil and silicon antifoam. ²²The pourpoint depressant was Infineum V387 available from Infineum UK Ltd. ²³Theviscosity modifier was Paralone 68530 available from Chevron Oronite.²⁴The base stock comprised an API Group II base stock.

Oils 5 and 6 include no boron (in order to maintain equivalentdispersant functionality in the compositions, boron-free dispersants areincluded in the compositions). Oils 5 and 7 contain no molybdenum. Thus,Oil 5 contains neither boron nor molybdenum, Oil 6 contains a relativelyhigh molybdenum dose but no boron, and Oil 7 contains a relatively highboron dose but no molybdenum. Oils 8 and 9 include boron and molybdenum.Oil 8 containing the same relatively high boron dose and a relativelyhigh molybdenum dose as Oils 7 and 6, respectively, and Oil 9 includinghalf the amount of boron and molybdenum.

The compositions were tested for LSPI event occurrence according to theASTM (Ford) LSPI test for applications claiming GF-6/API SP, the resultsbeing presented in Table 7. The tests were run in a matrix fashion in arandom order, with a reference oil run every five tests.

TABLE 7 Average LSPI Event Occurance Oil 5 Oil 6 Oil 7 Oil 8 Oil 9 14 816 4 6

The LSPI test results set out in Table 7 are also shown in matrix formatin FIG. 1. The lest results indicate no reduction in LSPI frequencythrough substantially increasing the boron content of the compositionfrom 0 ppm to 400 ppm in the absence of molybdenum, and a modestreduction in LSPI frequency (43% reduction) through substantiallyincreasing molybdenum content of the composition from 0 ppm to 700 ppmin the absence of boron. In contrast, the test results show asignificantly more substantial reduction in LSPI frequency (57%reduction) through only moderately increasing both the boron content andthe molybdenum content from 0 ppm to 200 ppm and 350 ppm, respectively.Furthermore, the test results show an even more significant reduction inLSPI frequency (71% reduction) through substantially increasing both theboron content and the molybdenum content from 0 ppm to 400 ppm and 700ppm, respectively. Surprisingly, the test results of Example 3 show asynergistic effect on LSPI frequency reduction resulting from thecombination of both boron and molybdenum in a lubricating oilcomposition.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims. Moreover, it is to be understood dratsuch optional integers or features, whilst of possible benefit in someembodiments of the invention, may not be desirable, and may therefore beabsent, in other embodiments.

What is claimed is:
 1. A method of reducing low-speed pre-ignition(LSPI) events in a direct-injection spark-ignition internal combustionengine comprising lubricating the crankcase of the engine with alubricating oil composition, the lubricating oil composition comprisinga boron-containing additive and a molybdenum-containing additive, saidlubricating oil composition having a molybdenum content of at least 150ppm by weight, based on the weight of the lubricating oil composition,and having a boron content of at least 150 ppm by weight, based on theweight of the lubricating oil composition.
 2. A method according toclaim 1, wherein, in operation, the engine generates a brake meaneffective pressure level of greater than 1,500 kPa, at engine speeds offrom 1,000 to 2,500 rotations per minute (rpm).
 3. A method according toclaim 1, wherein the lubricating oil composition has a molybdenumcontent of from 150 ppm to 1500 ppm by weight, based on the weight ofthe lubricating oil composition.
 4. A method according to claim 2,wherein the lubricating oil composition has a molybdenum content of from150 ppm to 1500 ppm by weight, based on the weight of the lubricatingoil composition.
 5. A method according to claim 1, wherein thelubricating oil composition has a boron content of from 150 to 1500 ppm,based on the weight of the lubricating oil composition.
 6. A methodaccording to claim 2, wherein the lubricating oil composition has aboron content of from 150 to 1500 ppm, based on the weight of thelubricating oil composition.
 7. A method according to claim 3, whereinthe lubricating oil composition has a boron content of from 150 to 1500ppm, based on the weight of the lubricating oil composition.
 8. A methodaccording to claim 4, wherein the lubricating oil composition has aboron content of from 150 to 1500 ppm, based on the weight of thelubricating oil composition.
 9. A method according to claim 1, whereinthe lubricating oil composition comprises a calcium detergent providingthe lubricating oil composition with a calcium content of from 0.08 to0.5 wt. %, based on the weight of the lubricating oil composition.
 10. Amethod according to claim 7, wherein the lubricating oil compositioncomprises a calcium detergent providing the lubricating oil compositionwith a calcium content of from 0.08 to 0.5 wt. %, based on the weight ofthe lubricating oil composition.
 11. A method according to claim 1,wherein the lubricating oil composition has a magnesium content of nomore than 0.12 wt. %, based on the weight of the lubricating oilcomposition.
 12. A method according to claim 10, wherein the lubricatingoil composition has a magnesium content of no more than 0.12 wt. %,based on the weight of the lubricating oil composition.
 13. A methodaccording to claim 11, wherein the lubricating oil composition has amagnesium content of less than 0.05 wt. %, based on the weight of thelubricating oil composition.
 14. A method according to claim 12, whereinthe lubricating oil composition has a magnesium content of less than0.05 wt. %, based on the weight of the lubricating oil composition. 15.A method according to claim 1, wherein the boron-containing additive Isone or more of: a borated dispersant, a borated dispersant viscosityindex improver, an alkali metal or an alkaline earth metal borate, aborated overbased metal detergent, a borated epoxide, a borate ester, asulfurised borate ester, or a borate amide; optionally wherein theboron-containing additive is one or more of a borated dispersant, aborate ester or a borated overbased metal detergent.
 16. A methodaccording to claim 1, wherein the molybdenum-containing additive is anoil-soluble or oil-dispersible organo-molybdenum compound, optionallywherein the molybdenum-containing additive is one or more of amolybdenum dithiocarbamate, a molybdenum dithiophosphate, a molybdenumdithiophosphinate, a molybdenum xanthate, a molybdenum thioxanthate, ora molybdenum sulfide.
 17. A method according to claim 1, wherein thelubricating oil composition has a phosphorus content of no more than0.12 wt. %, based on the weight of the lubricating oil composition. 18.A method according to claim 17, wherein the lubricating oil compositionhas a phosphorus content of no more than 0.08 wt. %, based on the weightof the lubricating oil composition.
 19. A method according to claim 13,wherein the lubricating oil composition has a phosphorus content of nomore than 0.08 wt. %, based on the weight of the lubricating oilcomposition.
 20. A method according to claim 18, wherein the lubricatingoil composition has a phosphorus content of no more than 0.06 wt. %,based on the weight of the lubricating oil composition,
 21. A methodaccording to claim 19, wherein the lubricating oil composition has aphosphorus content of no more than 0.06 wt. %, based on the weight ofthe lubricating oil composition.